This application claims priority of Korea patent Application No. 2001-12078, filed on Mar. 8, 2001.
The present invention relates to a polypropylene resin composition and more particularly, to the polypropylene resin composition comprising: (A) a propylene polymer comprising a propylene-ethylene copolymer having a certain limit viscosity alone and/or a propylene homopolymer having a certain pentad fraction (% mmmm); (B) an ethylene-xcex1-olefin copolymer rubber comprising ethylene-propylene copolymer rubber and ethylene-xcex1-olefin copolymer; (C) a styrene copolymer rubber; (D) a polypropylene modified with polar group-containing resin or a polyolefin polyol; and (E) an inorganic filler. The polypropylene resin composition provides superior in rigidity, scratch resistance, gloss, adhesion to paint to the conventional polypropylene resin compositions and further provides excellent laser scoring characteristics and improved impact strength at a low temperature thus, being useful for interior automotive parts such as instrument panels, especially an instrument panel integrally enclosing an air bag.
Polypropylene resins have been extensively used in exterior automotive parts including automotive bumpers and interior automotive parts including instrument panels and pillars, because they are excellent in flowability, impact strength, chemical resistance, and low-cost and have low specific gravity. However, in a case of interior automotive parts such as instrument panels, especially an instrument panel integrally enclosing air bag, an air bag is mounted within the instrument panel after the portion where the air bag is stowed is cut and then concealed that portion thus, resulting in vexatious complication and poor appearance. On the other hand, when an air bag is installed integrally within the instrument panel to remove such complications, there is a possibility of no opening of the air bag in an accident. Therefore, it is required to preweaken components overlaying an air bag enclosed within the instrument panel by scoring with the use of laser beam to be properly deployed in emergency. Accordingly, the instrument panel integrally overlying an air bag is expected to have excellent physical properties and adhesion to the paint and additionally stand laser scoring for the air bag to properly open in emergency. And further, it is required to exhibit excellent impact strength at a low temperature not to form broken pieces thereof when the air bag inflates.
There have been development of polypropylene resin compositions for interior automotive parts such as an instrument panel which provide good rigidity and physical properties and thus suitable for direct painting without a pretreatment but there is no development of polypropylene resin composition suitable for an instrument panel integrally enclosing an air bag. The inventors of the present invention have disclosed the polypropylene resin composition suitable for the instrument panel having excellent physical properties and adhesion to paint in U.S. patent application Ser. No. 09/749,698. However, the polypropylene resin composition disclosed in U.S. patent application Ser. No. 09/749,698 has excellent rigidity, physical properties and adhesion but it becomes dangerous for broken pieces formed with the inflation of an air bag due to lowered impact strength at a low temperature after post-treatment with laser beam.
Therefore, it is highly demanded to develop a polypropylene resin composition having excellent physical properties, adhesion to paints and additionally superior low-temperature impact strength required for an air bag deployment opening in an automotive industry.
An object of the present invention is to provide a polypropylene resin composition having excellent physical properties such as rigidity, scratch resistance, gloss, and adhesion to paints, laser scoring characteristics and highly reinforced low-temperature impact strength by comprising: a propylene polymer selected from the group consisting of a propylene-ethylene copolymer, and/or a propylene homopolymer; an ethylene xcex1-olefin copolymer rubber comprising an ethylene-propylene copolymer rubber and ethylene-xcex1-olefin copolymer; a styrene copolymer rubber, a polar group-containing resin, and an inorganic filler.
The present invention is characterized by a polypropylene resin composition comprising;
(A) 30 to 70 wt. % of a propylene polymer comprising 0 to 30 wt. % of propylene homopolymer and 70 to 100 wt. % of propylene-ethylene copolymer;
(B) 10 to 30 wt. % of an ethylene xcex1-olefin copolymer rubber comprising 60 to 95 wt. % of ethylene-propylene copolymer rubber and 5 to 40 wt. % of ethylene xcex1-olefin copolymer;
(C) 1 to 10 wt. % of a styrene copolymer rubber comprising 10 to 50 wt. % of polymer blocks of styrene or its derivative, 50 to 90 wt. % of polymer blocks copolymerized with at least one selected from ethylene, isoprene, butylene, butadiene, and propylene;
(D) 1 to 7 wt. % of polar-group containing resin comprising a modified polypropylene grafted to 0.5 to 6.0 wt. % of graft ratio, a polyolefin polyol, or mixture thereof; and
(E) 10 to 40 wt. % of an inorganic filler selected from the group consisting from talc, barium sulfate, potassium carbonate, and wollastonite.
The polypropylene resin composition of the present invention provides an interior automotive material suitable for an instrument panel integrally enclosing air bag with an injection molding. The instrument panel integrally enclosing an air bag with excellent laser scoring property and low-temperature impact strength is prepared from the molded article by coating without primer treatment and mounting an air bag.
Hereunder is given the detailed description of each component comprising the polypropylene resin composition of the present invention.
(A) Propylene Polymer
A propylene copolymer of the present invention is a crystalline polymer comprising a propylene-ethylene copolymer containing ethylenes and/or a propylene homopolymer.
Said propylene homopolymer has higher than 96% of pentad fraction (% mmmm) measured with 13C-NMR, preferably higher than 96.5%, and more preferably higher than 97%. If the pentad fraction is lower than 96%, the rigidity and heat resistance of the polypropylene resin composition become inferior. Also, the limit viscosity [xcex7] of said propylene polymer of the present invention measured in 135xc2x0 C. of decalin is in the range of 0.7 to 2.5 dl/g, preferably in the range of 0.85 to 2.2 dl/g, and more preferably in the range of 0.9 to 2.0 dl/g. If the limit viscosity [xcex7] is lower than 0.7 dl/g, the impact strength of the formed polypropylene resin composition worsens, and if it exceeds 2.5 dl/g, the flowability becomes poor, so that the quality of the finally formed product worsens and the working condition becomes poor.
Said propylene-ethylene copolymer includes 3 to 20%, and preferably 5 to 15% of an ethylene content. The limit viscosity [xcex7] of propylene-ethylene block copolymer of the present invention measured in 135xc2x0 C. of decalin is in the range of 3.0 to 6.0 dl/g, preferably higher than 3.5 dl/g, and more preferably higher than 4.0 dl/g.
For a well-balanced properties of impact strength and fluidity, the composition of the propylene homopolymer and the propylene-ethylene copolymer is recommended to be in the range of 0 to 30:70 to 100 wt. %, and more preferably in the range of 0 to 20:80 to 100 wt. %. While the propylene homopolymer provides superior rigidity and heat resistance, it has poor impact strength. On the other hand, the propylene-ethylene copolymer provides improved impact strength, especially at a low temperature but it has poor formability, rigidity and heat resistance. Therefore, they can complement each other when mixed together.
The content of the propylene copolymer to the entire polypropylene resin is recommended to be in the range of 30 to 70 wt. %, more preferably in the range of 45 to 65 wt. %. If it is used more then 70 wt. %, the impact strength becomes impaired. On the other hand if it is used lower than 30 wt. %, the formability becomes poor.
(B) Ethylene-xcex1-Olefin Copolymer Rubber
An ethylene-xcex1-olefin copolymer rubber (B) of the present invention comprises an ethylene-propylene copolymer rubber and ethylene-xcex1-olefin copolymer and is added to increase the impact strength by providing elasticity to the entire polypropylene resin composition.
The Mooney viscosity [xcex7]ML1+4 (125xc2x0 C.) of the ethylene-propylene copolymer rubber (EPR) is in the range of 50 to 80 dl/g, preferably in the range of 55 to 70 dl/g. If the Mooney viscosity is higher than 80 dl/g, an appearance is inferior due to poor dispersion and the mechanical properties also become worsen. On the other hand, if it is less than 20 dl/g, the impact strength is lowered. The ethylene-propylene copolymer rubber (EPR) includes 20 to 80 wt. % of a propylene content, preferably 40 to 80 wt. %. If the content of propylene is lower than 20 wt. %, the impact strength worsens, and if it exceeds 80 wt. %, the rigidity worsens.
In particular, the ethylene-xcex1-olefin copolymer of the present invention, is ethylene 1-butene (EBM) or ethylene 1-octene copolymer (EOM) and it is preferred to contain 12-45 wt. % of an xcex1-olefin content. Said EBM having 12-45 wt. % of a butene content, preferably 15-20 wt. % and 0.5-10 g/10 min of a melt index, preferably 1-5 g/10 min, is preused. Said EOM having 15-45 wt. % of an octene content, preferably 25-35 wt. %, 1-50 dl/g of limit viscosity [xcex7]ML1+4 (121xc2x0 C.), preferably 1.5-35 dl/g, and 0.86-0.91 g/cm3 of a density, preferably 0.87-0.90 g/cm3, is used.
Ethylene-propylene copolymer rubber (EPR) and ethylene xcex1-olefin copolymer are mixed in the range of 60 to 95:40 to 20 wt. %, preferably in the range of 80 to 85:20 to 15 wt. % for the good of impact strength and rigidity balance. If ethylene-propylene copolymer rubber (EPR) is used solely, the rigidity worsens; and if xcex1-olefin copolymer is used solely, the impact resistance worsens.
The content of ethylene-xcex1-olefin copolymer rubber to the entire polypropylene polymer is recommended to be in the range of 10 to 30 wt. %, preferably in the range of 15 to 25 wt. %. If the said content is below 10 wt. %, the rigidity and formability worsen; and if it exceeds 30 wt. %, the impact strength worsens.
(C) Styrene Copolymer Rubber
A styrene copolymer rubber of the present invention comprises a polymer block of styrene or its derivate; and a polymer block of at least one selected from ethylene, isoprene, butadiene, and propylene to improve the impact strength without reducing the rigidity.
The copolymer rubber used in the present invention has higher than 97% of unsaturated bonds and an xe2x80x9ca-b-axe2x80x9d linear type or non-linear type, wherein xe2x80x9caxe2x80x9d block is formed from styrene or its derivative, xe2x80x9cbxe2x80x9d block is formed from at least one selected from ethylene, isoprene, butadiene, and propylene. xe2x80x9caxe2x80x9d Block is used to enhance rigidity, gloss, tensile strength and hardness of the resin composition and xe2x80x9cbxe2x80x9d block is used to improve compatibility with the olefin resin composition. xe2x80x9caxe2x80x9d Block is used in the range of 10 to 50 wt. %. If a content of xe2x80x9caxe2x80x9d block is less than 10 wt. %, the rigidity and hardness are inferior. On the other hand, if it is more than 50 wt. %, the compatibility to olefin resin composition becomes poor, resulting in poor impact strength.
A content of styrene copolymer rubber to the entire polypropylene polymer is recommended to be in the range of 1 to 10 wt. %, preferably in the range of 1.5 to 7 wt. %. If the said content is higher than 10 wt. %, the gloss worsen; and if it is less than 1 wt. %, the elongation, etc is impaired.
(D) Polar Group-Containing Resin
A polar group-containing resin used in the present invention is a modified polypropylene, a polyolefin polyol, or a mixture thereof.
The modified polypropylene is a polypropylene copolymer grafted with dimethylol-p-octylphenol, an unsaturated carbonic acid or a derivative thereof, wherein examples of the unsaturated carbonic acid include maleic acid, acrylic acid, methacrylic acid, anhydrous maleic acid, and mixtures thereof. Here, a graft ratio is recommended to be 0.5 wt. % or higher, preferably 1.5wt. % or higher. If the graft ratio is lower than 0.5wt. %, it can be scraped by external impact due to poor adhesion to paint.
The polyolefin polyol of the present invention has polar hydroxyl (xe2x80x94OH) groups bonded at both ends of the saturated carbohydrate backbone having 150 to 200 carbon atoms. The polyolefin polyol is a low-molecular polymer with 10 to 16 poise (100xc2x0 C.) of viscosity, 20 to 80 KOH mg/g of hydroxyl value. If the hydroxyl value of polyolefin polyol is lower than 20 KOH mg/g, the adhesion to paint becomes impaired. Otherwise if it exceeds 80 KOH mg/g, the adhesion to paint improves but the rigidity and impact strength worsen.
The modified polypropylene and polyolefin polyol according to the present invention can be used solely or mixed together. When used solely, the modified polypropylene is recommended to be in the range of 1 to 10 wt. %, preferably in the range of 1 to 5 wt. % to the entire polypropylene composition; and the polyolefin polyol is recommended to be in the range of 1 to 5 wt. %, preferably in the range of 1 to 3 wt. % to the entire polypropylene composition. When the two components are mixed together, the content of the mixed resin is recommended to be in the range of 1 to 7 wt. % to the entire polypropylene resin composition. If the content exceeds 7 wt. %, the impact property and rigidity may worsen.
(E) Inorganic Filler
An inorganic filler having an average particle size of 0.5 to 7 xcexcm of the present invention is selected from the group consisting of talc, barium sulfate, calcium carbonate and wollastonite. Especially, talc with smaller average particle size than 7 xcexcm is preferable in view of dispersion and other properties.
This inorganic filler is added in the range of 10 to 40 wt. % to the entire polypropylene resin. If the content is lower than 10 wt. %, the rigidity and heat resistance worsen, and if it exceeds 40 wt. %, the impact strength worsens.
Other additives, used by one having ordinary skill in the art, such as an anti-oxidant, a neutralizer, an anti-static agent, and a nucleating agent may be arbitrarily incorporated in an appropriate content not to obstruct the above-mentioned object of the present invention. Examples of the anti-oxidant are phenols, phosphates, and thiodipropionate synergists and examples of the neutralizer are calcium stearate and zinc oxide.
The polypropylene resin composition comprises the components (A) to (E) in the respective prescribed amount and if desired, an additional additive has a melt index of 3 to 40 g/10 min. When it is lower than 3 g/10 min, processability may be degraded and the flow mark of the product may occur. On the other hand, when it is higher than 40 g/10 min, the physical properties such as strength, rigidity, and impact strength become poor.
The method for preparing the polypropylene resin composition of the present invention is not limited to any special method. For example, components (A), (B), (C), (D), and (E) of the polypropylene resin composition according to the present invention can be prepared by a conventional mechanical mixing method. To be specific, general melt mixing machines such as Bambury mixer, single-screw extruder, twin-screw extruder and multi-screw extruder can be employed. Here, the mixing temperature is recommended to be in the range of 170 to 240xc2x0 C.
The resin composition of the present invention can be subjected to the production by any of various molding techniques including extrusion, blow molding, injection molding, and sheet molding. Of these molding techniques, injection molding is preferably used.
The formed interior automotive parts prepared from the polypropylene resin composition of the present invention can be directly painted using modified acryl paint or urethane paint without the pretreatment. And then it is scored using the laser beam around an air bag. Since a particular infrared frequency (943 cmxe2x88x921) is used to have an even thickness after scoring, the resin composition has a high penetration to the used infrared frequency. If the penetration is low, it becomes impossible to control the thickness, resulting in uneven thickness, no opening of the air bag, and the formation of broken pieces if it is opened. Therefore, the test for proper opening of the air bag is performed.
Hereunder is given a more detailed description of the present invention using examples. However, it should not be construed as limiting the scope of this invention.